Alcohol/ether separation by pervaporation. High performance membrane design

Several routes were investigated to design high performance membranes for t he separation of tert-butyl ethers (octane enhancers) from alcohols by perv aporation. These routes aim at incorporating Lewis base groups into good fi lm-forming polymers with different structures. The Lewis base groups showed a high affinity to alcohols in screening tests, thus imparting high pervap oration selectivity to the polymer materials. They led to several membranes able to extract pure ethanol out of the azeotropic mixture, but with very low permeation rates. Further modifications of the polymer structure allowe d us to synthesize materials with greatly enhanced transfer rates and with acceptable selectivity for industrial applications. Structure-property rela tionships were derived from sorption and pervaporation data for a qualitati ve prediction of the effect of polymer structure on the flux and selectivit y. For these solvent-polymer systems the diffusion phenomenon appears to fu rther improve the pervaporation selectivity for alcohol compared with that given by the sorption process at the membrane face.